Recovery and recrystallization of warm-rolled tungsten during helium thermal desorption spectroscopy annealing

Tungsten has been perceived as one of the most promising plasma-facing materials for future fusion reactors. Its behavior under helium irradiation has been extensively studied. In this work, we focus on the recovery and recrystallization of helium-implanted surface grains in warm-rolled polycrystalline tungsten. Mechanically polished specimens with and without 40 keV helium implantation were heated to 1650 °C during helium thermal desorption spectroscopy experiment. Our results suggest that recovery and recrystallization occurred via subgrain coarsening and removal of low-angle grain boundaries in as-polished specimen. Its average grain size increased from 1.70 to 8.89 μm, and its fraction of low-angle grain boundary decreased from 0.77 to 0.29. By contrast, little changes of grain size and grain boundary misorientation angle were found in helium-implanted surface grains. Such enhanced thermal stability is attributed to the pinning effect of helium bubbles on grain boundaries, and the underlying mechanism is discussed based on the proposed model of cellular microstructure.